Closed aerosol development



2 Sheets-Sheet 1 INVENTOR. DANIEL J. DONALIES 53?? 561 z; ATTORNEY Oct. 4, 1966 D. J. DONALIES CLOSED AEROSOL DEVELOPMENT Filed Sept. 30, 1963 Oct. 4, 1966 D. ,1. DONALIES 3,276,425

CLOSED AEROSOL DEVELOPMENT Filed Sept. 30, 1963 2 Sheets-Sheet 3 1N VENTOR.

A T TORNEY DANIEL J. DONALIES BY United States Patent York Filed Sept. 30, 1963, Ser. No. 312,601 6 Claims. (131. 118-637) This invention relates to xerography and particularly to improved apparatus for the development of electrostatic images supported on an image bearing member.

In the process of xe-rography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1942, a xerographic pla-te including a layer of photoconductive insulating material has a uniform electrostatic field applied thereto as by charging and is then exposed to an activating radiation image of the subject matter to be reproduced, usually by conventional projection techniques. Exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is efiected with an electrostatically charged, finely-divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed image is usually transferred to a support surface to which it may be afiixed by any suitable means.

Various systems are known for developing electrostatic images including cascade, powder cloud, brush, liquid immersion etc., each having particular application for which they are most appropriately suited as is well known in the art.

Typical prior art type powder cloud systems are disclosed in US. Patents 2,815,330; 2,859,127; 2,943,950 and 2,965,069. In a powder cloud system as will be understood, a powder cloud is generated by agitating a mass of dry electrosco-pic material in a confined space. The cloud so produced is charged and then contacted with the electrostatic latent image. This makes possible the realization of extremely high resolutions such as 1200 or more lines per inch. Accordingly, the powder cloud system has been found to be highly suitable for developing sensitive charge gradients such as are associated with continuous tone type reproductions. However, despite the known advantages of the powder cloud system, the equipment associated therewith for generating, charging and directing the flowing of the powder cloud has heretofore been rather complicated and at the same time, costly to fabricate.

Now in accordance with the instant invention, there is provided a novel form of powder cloud apparatus for developing electrostatic latent images on an image bearing member. The apparatus hereof is novel, compact, and without the attending prior apparatus complexities as to be substantially less costly to produce than comparable apparatus of the prior art. At the same time, the apparatus is highly efiicient producing high quality, high fidelity developments of electrostatic latent images that can subsequently be transferred or otherwise utilized as is known in the art.

Accordingly, it is an object of the invention to provide novel apparatus for the development of electrostatic latent images on an insulating support member.

It is a further object of the invention to provide a novel form of powder cloud generating apparatus that is simpler and less costly to fabricate than apparatus heretofore for developing electrostatic latent images on an image bearing member.

These and other objects will appear clearly in the 3,276,426 Patented Oct. 4, 1966 following specification when read in conjunction with the folloing drawings, the novel features being pointed out in the claims in the specification.

In the drawings:

FIG. 1 is an isometric View showing an apparatus embodiment in accordance with the inevntion; and,

FIG. 2 is a side elevation partly in section of the embodiment shown in FIG. 1.

The apparatus of the invention will now be described with reference to the drawings. As there shown, the apparatus is comprised of a developing chamber, generally designated 10, adapted for placement on a table or other suitable horizontal surface 11. The developing chamber is comprised of a top wall 12 bolted, as by recessed screws 13, to a bottom wall 14 resting on the table. At both ends, as viewed in the drawings, and along the sides, the walls form an internal air-tight seal by means of a compressed gasket member 15. In the center portion between the walls, there is formed an air passage defined generally by the inside opposing surfaces, as well as the side edges of walls 12 and 14, the former of which has been milled or otherwise cut to effect a thinner cross-section through the middle than at the ends.

For reasons that will be understood, the inside surfaces of the air passage are lined with a thin sheet or layer of material, designated and 26, that is characterized in its ability to impart a proper triboelectric effect to developer moving in contact thereagainst.

For supporting an insulating member having an image to be developed and shown as a xerographic plate 24, there is provided a rectangular opening 21 at approximately the center of the top wall (shown occupied by the plate), the sides of which include shoulder supports 22 and 23. The xerographic plate has a companion shoulder about its periphery adapted to seat on shoulder 22 whereby the photoconductive insulating surface 21 of the plate bearing a developable image faces inwardly of the air passage approximately flush or coplanar with the top inside surface thereof. A removable backing plate having a hand knob 31 is adapted to seat via gasket member 32 against the top side (in the position shown) of the xerographic plate to maintain and urge the plate into secured position. To secure an air tight relation of the plate to the air passage, there is provided a pair of U-clamps 33 that can be tightened down via thumb screws 34 located along opposite sides of the opening. Insertion or removal of a xerographic plate to or from its development position is eifected by first loosening screws 34 permitting clamps 33 to be withdrawn free of the opening when gripped by lip 35 to the extent permitted by elongated oval slots 36. With backing plate 30 removed, xerographic plate 24 can then manually be inserted or removed.

For the transmission or injection of pressurized air into the chamber, the top wall includes localized openings 44B and 41 extending vertically through the wall and communicating with the air passage at substantially opposite ends thereof. Secured by means of an annular ring 42 in air tight relation above openings and 41 for the generation of pressurized air are expandable air bellows members 43 and 44, respectively. Each bellows is formed of a resilient compressible material such as a plastic or rubberized coating encasing a metal coil spring that regains its normal length dimension on removal of a compressing force therefrom or can operate by forced expansion as shown. As will be understood, each bellows is intended to be compressed alternately so that one is being compressed as the other is being expanded in order to effect alternating reversible contained air flow in the air passage 20.

To compress the bellows, each bellows is capped by a plate 50 supported for vertical travel on four vertical guide posts 51 secured at their lower ends to top wall 12 and at their upper ends in a structural plate member 52. Each cap 50 includes a bifurcated flange 53 drilled to receive a pin 54 for connecting the cap to an arm 55 in turn connected via a pin -6 to opposite ends of a rocker arm 57 mounted on rotatable shaft 7ft journalcd in bearing block 71.

Oscillation of the rocker arm, in order to actuate the bellows with a reciprocating motion, originates from a motor 60 mounted on a vertically extending side wall 61 and operative under control of a timer, counter or the like, The motor shaft 62 extends via a right angle extension through the side wall and is adapted to rotate an eccentric element 63 secured thereto. A crank 64 is connected at its lower end to a pin 65 of the eccentric and at its upper end, is similarly connected by means of a pin 66 to the rocker arm. As the eccentric rotates, the crank is caused to oscillate rocker arm 57 to impart a reciprocation to arms 55 alternately effecting compression and expansion of the individual bellows members. As each bellows begins compression, it generates a flow of pressurized air through its respective opening below into and through air passage and into the opposite bellows beginning its expansion stage.

Developer, designated 58, by which the electrostatic latent image on plate 24 is rendered visible, is generally retained along the surface of lower lining 26. Preferably the developer is precha rged to negative polarity prior to its being placed within the apparatus as by triboelectrification, corona charging, or the like. It may also be triboelectrically charged as by brushing in place on the lower lining before assembly of the latter into the apparatus. The developer may be comprised, for example, of finely-divided pigmented resin particles termed toner of approximately 5 to about 30 microns consisting of a finely-divided uniform mixture of pigment in a non-tacky low-melting resin as disclosed in US. Reissue Patent 25,136. Other developers including powdered charcoal or the like may also be used as is known in the art. As either bellows is compressed developer is blown as an aerosol toward and into the opposite bellows. In so doing, the toner particles pass in contact with the liner members and 26 as well as passing in contact over the surface of xerographic plate 24.

The liner members are characterized in their ability to effect triboelectrification of the toner particles to the appropriate polarity for effecting development of the electrostatic latent image. Various materials to comprise the liner are known in the art as being particularly suited for the purpose including coated papers, as for example, disclosed in Us. Patent 2,895,847; rubberized hospital sheeting, as manufactured by the Plymouth Rubber Company; a baryta paper, etc. It is to be understood that either positively charged or negatively charged powder may be employed herein for effecting development. Desirably, the surface of the liner should be selected from its position in the triboelectric series to acquire opposite triboelectric relationship to the toner such that for negatively charged powder, the liners should acquire a positive charge with respect to the powder and vice versa. Cellulose sheets of barium sulphate in a gelatin binder and known as baryta paper acquiring a positive charge was found to function well in imparting the proper triboelectric relationship to the toner particles for operation in the apparatus in accordance with the invention. As the toner particles pass over the electrostatic latent image, development thereof is effected.

In operation, a xerographic plate on which an electrostatic latent image has been previously formed is secured image-side down in opening 21. When motor 60 is energized, one of bellows 43 or 44 begins compressing while the other begins expanding resulting in reversal flow of a developer aerosol in a closed system back and forth through the air passage 20 in contact with the plate image to effect image development. The ultimate fidelity of the developed image achieved by the apparatus is to some degree a function of various factors including the number of aerosol. passes in each direction per development cycle, the quantity or concentration of developer flowing per pass, the air velocity, etc. Obviously, many usable and optimum combinations of these different factors can be empirically determined by one skilled in the art. In the embodiment described, high quality image development in excess of 10 line pairs per mm. were produced with a height dimension of the air passage of approximately A; inch using approximately 3 grams of developer, for 15 passes on generation of a pressure differential of approximately 1.2 p.s.i.g. per bellows compression to effect an aerosol velocity in the passage of about 450 inches per second.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for developing an electrostatic latent image on a xerographic plate comprising in combination:

(a) an enclosed substantially airtight chamber includ ing at least partially spaced-apart parallel walls defining an air passage therebetween;

(b) openings defined in said chamber extending from an external surface thereof and communicating to said air passage from substantially opposite ends thereof;

(c) developer support means to support and charge a distributed quantity of electroscopic developer material substantially along an inside surface of a wall forming said air passage;

((1) xerographic plate support means in one of said parallel walls between said openings to support a xerographic plate with its developnble surface facing inward of and exposed to said air passage; and

(e) means to apply a quantity of pressurized air alternately to opposite of said openings whereby developer is caused to flow in an aerosol from its support means in said air passage in alternate directions in contact past a xerographie plate to effect development of an electrostatic latent image thereon.

2. The apparatus according to claim 1 in which the application of pressurized air is effected by air bellows secured in air tight relation about each of said openings and including means to compress and expand the bellows at opposite openings in opposing relation to each other.

3. The apparatus according to claim 2 including an oscillating rocker arm assembly operatively engaging each air bellows to reciprocably compress and expand the different bellows in timed relation to each other.

4. Apparatus for developing an electrostatic latent image on a xerographic plate comprising in combination:

(a) an enclosed substantially airtight chamber including spaced-apart parallel walls defining an air passage therebetwcen and adapted to contain a quantity of distributed electroscopic developer material;

(b) openings defined in said chamber extending from an external surface thereof and communicating to said air passage from substantially opposite ends thereof;

(0) at least one section of charging material arranged along said air passage and adapted to triboelectrically charge developer particles passing in contact therewith;

(d) xerographic plate support means in one of said parallel walls between said openings to support a xerographic plate with its dcvelopable surface facing inward of and exposed to said air passage; ant

(e) means to apply a quantity of pressurized air alter- 3,276,426 5 6 nately to opposite of said openings whereby develand including means to compress and expand the bellows oper is caused to flow as an aerosol in said air pasat opposite openings in opposing relation to each other. sage in alternate directions in contact past a xerographic plate to efiect development of an electro- References Cited y the Examiner static latent image thereon.

5 A t 1 4 h h 5 UNITED STATES PATENTS pparatus accor mg 0c aim 1nw 1c sai c argg m rial comprises thin layers extending at least i f g g- 3 partially and substantially along at least one inside surface 2895847 7/1959 M: o 117 17 5 of awauforming Said airpassage' 2 998 802 9/1961 Hai ris etal 1 17-Hs X 6. The apparatus according to claim 5 in which the application of pressurized air is efiected by air bellows 10 CHARLES A WILLMUTH Primary Examiner secured in air tight relation about each of said openings 

1. APPARATUS FOR DEVELOPING AN ELECTROSTATIC LATENT IMAGE ON A XEROGRAPHIC PLATE COMPRISING IN COMBINATION: (A) AN ENCLOSED SUBSTANTIALLY AIRTIGHT CHAMBER INCLUDING AT LEAST PARTIALLY SPACED-APART PARALLEL WALLS DEFINING AN AIR PASSAGE THEREBETWEEN; (B) OPENINGS DEFINED IN SAID CHAMBER EXTENDING FROM AN EXTERNAL SURFACE THEREOF AND COMMUNICATING TO SAID AIR PASSAGE FROM SUBSTANTIALLY OPPOSITE ENDS THEREOF; (C) DEVELOPER SUPPORT MEANS TO SUPPORT AND CHARGE A DISTRIBUTED QUANTITY OF ELECTROSCOPIC DEVELOPER MATERIAL SUBSTANTIALLY ALONG AN INSIDE SURFACE OF A WALL FORMING SAID AIR PASSAGE; (D) XEROGRAPHIC PLATE SUPPORT MEANS IN ONE OF SAID PARALLEL WALLS BETWEEN SAID OPENINGS TO SUPPORT A XEROGRAPHIC PLATE WITH ITS DEVELOPABLE SURFACE FACING INWARD OF AND EXPOSED TO SAID AIR PASSAGE; AND (E) MEANS TO APPLY A QUANTITY OF PRESSURIZED AIR ALTERNATELY TO OPPOSITE OF SAID OPENINGS WHEREBY DEVELOPER IS CAUSED TO FLOW IN AN AEROSOL FROM ITS SUPPORT MEANS IN SAID AIR PASSAGE IN ALTERNATE DIRECTIONS IN CONTACT PAST A XEROGRAPHCI PLATE TO EFFECT DEVELOPMENT OF AN ELECTROSTATIC LATENT IMAGE THEREON. 